The present invention relates to a new and improved construction of an electrodynamic force measuring apparatus comprising a force coil arranged in a stationary magnetic field and movable out of a null position by the action of the force which is to be measured, this force coil is supplied with a current through the agency of an amplifier as a function of its deviation out of the null position as detected by a feeler, this current producing, under the action of the stationary magnetic field, a restoring force which forces back the force coil into the null position.
With such a force measuring apparatus the current delivered to the force coil by the amplifier serves directly or indirectly, for instance in the form of a voltage which is tapped-off across a resistor, as a measure for the force which is to be measured. The relationship of the current intensity-force is then linear when the influencing of the stationary magnetic field by the secondary magnetic field produced by the current flowing through the force coil is practically negligible. However, this is only then the case with smaller forces, also with smaller currents. On the other hand, with larger forces the magnetic field generated by the current flowing in the force coil must be vectorially added to the stationary magnetic field, producing a resultant magnetic filed possessing a direction deviating from the stationary magnetic field. The restoring force acting upon the coil is however --apart from the current intensity of the current flowing through the force coil -- dependent upon the resultant magnetic field. Consequently, it will be appreciated that the change of the direction of the resultant magnetic field has the result that, with larger forces, there is no longer maintained the linear relationship between the current and the force which is to be measured.